1. Field of the Invention
The present invention is related to reflected light analysis. More particularly, the present invention is related to calibration of a reflection imaging spectrophotometer.
2. Related Art
Quantitative spectrophotometry requires a means for calibrating the detection subsystem of the spectrophotometer and for verification of the calibration. One approach to calibration involves the insertion of two or more standards of known reflectance in the measurement path and measuring the resultant detected signals from each. These standards may include, for example, a blank (i.e., a standard with zero absorption and full reflectance) plus one or more standards having other known optical densities.
Such an approach is complicated by the fact that the nature of the reflecting surface may influence the result. Thus, a standard reflecting surface is typically needed in addition to the optical density calibration standards themselves. Transfer of calibration from one reflecting surface to another, however, is not generally possible. A reflection imaging spectrophotometer that is calibrated with respect to one reflecting surface will not necessarily be calibrated correctly with respect to another reflecting surface. Hence a reflection imaging spectrophotometer that is calibrated with respect to some standard reflecting surface will not necessarily be calibrated correctly with respect to an actual subject. Moreover, control of the reflecting surface is not possible when performing reflection imaging spectrophotometry of living human tissue. A method is therefore needed to provide standards for calibration of reflection imaging spectrophotometers intended for such applications.